Rolling mill for producing constant gauge



Feb. 24, 1970 M. D. STONE ROLLING MILL FOR PRODUCING CONSTANT GAUGE 3Sheets-Sheet 1 Filed Aug. 21. 1967 INVENTOR. MORR/S 0. arc/v5 J QMATTORA/EV.

Feb. 24, 1970 M. D. STONE ROLLING MILL FOR PRODUCING CONSTANT GAUGEFiled Aug. 21. 1967 3 Sheets-Sheet 2 wm bw INVENTOR.

E W M m. M. 4 M

Feb. 24, 1970 M. D. STONE 3,496,743

ROLLING MILL FOR PRODUCING CONSTANT GAUGE Filed Aug. 21. 1967 :sSheets-Sheet s INVENTOR. MORRIS 0. STONE ATTOR/VfY.

United States Patent C U.S. Cl. 728 14 Claims ABSTRACT OF THE DISCLOSUREThe invention relates to a rolling mill of the type designed to producea constant thickness workpiece, such as metallic strip. The mill isprovided with a piston cylinder assembly for subjecting a first group ofmill parts, such as the bearing chock assemblies of one of the rolls, toa roll gap controlling force which is applied in a direction to resistthe rolling force of the mill. The cylinder is constructed and arrangedso that the force difference between its total force and the rollingforce is applied to a second group of mill parts, which may include atension or compression member. In this mill construction only a portionof the housing of the mill is subject to the rolling force.

In one form there is provided in a rolling mill having a housing, anelongated window in said housing, a pair of rolls between which arolling force is developed, including mounting means for each rollreceived in said window of said housing, wherein a portion of thehousing receiving the mounting means and said mounting means is subjectonly to the rolling force of the mill, means arranged at one end of saidwindow of said housing and between one of the mounting means and housingfor applying to a first group of mill parts, including one of saidmounting means, a substantial part of a roll ga-p controlling force,said force being applied in a direction to resist the rolling force ofthe mill, the force applying means being constructed and arranged sothat the force differential between its total force and the rollingforce is applied to a second group of mill parts, which excludes atleast said other mounting means, and wherein the elastic characteristicsof said two groups of mill parts have a predetermined relationship.

This rolling mill can be employed in combination with a control meansfor continually measuring the force imposed on either said first orsecond group of parts and varying the applying force proportional to achange in the force being imposed on said first or second group of millparts to maintain a predetermined relationship between either of theseforces and the applied force.

In another form, the present invention provides in a rolling mill, orlike apparatus, having a housing, a pair of rolls between which arolling force is developed including means arranged in said housing atone side thereof for applying to a first group of mill parts, includingsaid mounting means, a substantial part of a roll gap controlling force,said roll gap controlling force being applied in a direction to resistthe rolling force of the mill, the force applying means beingconstructed and arranged so that the force difierential between itstotal force and the rolling force is applied to a second group of millparts, which excludes at least one of said mounting means, and whereinthe elastic characteristics of said two groups of mill parts have apredetermined relationship, means separate from said force applyingmeans and associated with the mounting means arranged on the side of thehousing opposite said force applying means for adjusting the associatedmounting means and its roll to adjust the position of the rollindependent of said force applying means.

This rolling mill can be employed in a combination with a control meansfor continually measuring the force imposed on either said first orsecond group of parts and varying the applying force proportional to achange in the force being imposed on said first or second group of millparts to maintain a predetermined relationship between either of theseforces and the applied force.

In a still further form of the invention said second group of mill partscomprises one or more tension rods associated with the lowest rollassembly of the mill, said tension rod subject to a tension force bysaid force applying means, and wherein the tension imposed on saidtension rods is measured by a force measuring means. In certain cases aspring or equivalent device can be used in conjunction with the tensionrods compressible by said rods to give added flexibility to the system.

In still another form of the present invention, there is providedalternately either a force measuring device associated with the tensionrods or with the mill housing that receives the separating force fromthe roll assemblies.

A still further object of the present invention is to provide in arolling mill of the above-described construction a readily yieldablemeans received in the housing of the mill and so associated with theforce applying means to be subject to a compression force. In one formthe housings are provided with projections having openings to whichthere are received a plurality of springs, one end of which engages oneof the roll chocks of the roll assembly, this spring being compressed bythe application of said force applying means and wherein said housingprojections are in the vicinity of the work rolls of the mill.

In another form the housing projections are at the base of the millwherein the springs engage a member associated with said force applyingmeans and is compressible upon the movement thereof.

In one form the yieldable means is arranged between the mill screw and acrosshead against which a compression force is exerted.

A still further embodiment of the present invention comprises, either atthe top or bottom of a rolling mill, a pair of substantially parallelarms connectable to one of the roll chocks of the mill and extendingthrough or alongside the housing at which place they are connected witha cross member, means for adjusting the cross member relative to thepass line of the mill in which construction the force applying means inapplying a force on the roll chock to which the arms are associatedimposes a tension force on said arms, a portion of which is taken intothe cross member and into the housing.

As noted above, the present invention relates to a rolling mill forproducing constant gauge and, more particularly, uniformity oflongitudinal gauge, such as, metallic sheet or strip. It has been wellrecognized for many years that the degree of gauge accuracy in a rollingmill is dependent upon the stiffness of the mill, i.e. to say, theresistance the mill has to stretch under the rolling load generated inthe rolling of the material. ln this regard the art early in its historysought to add stiffness to the mill by providing one or more backuprolls for the reducing rolls. The most common for-m of such a mill isthe well known and universally employed 4-high mill. While themulti-high mill improved the stillness of the rolls and, hence, of themill and yielded a more uniform product, it leaves much to be desired.This is by reason of the fact that, notwithstanding the added stillnessafforded by the backup rolls, the rolls and housing and other componentsstretch considerably under the rolling load, which stretch varies as therolling load varies, resulting in a product having a non-uniform gauge.

Since the housing itself represents a substantial amount of the elasticstretch of the mill, the prior art sought to eliminate the housing as afactor in the obtaining of uniform gauge by providing a prestressingmeans, an example of which is shown in U.S. Patent No. 581,078 issued toF. Menne on Apr. 20, 1897. This, too, was an improvement in obtainingmore uniform gauge. However, since it did not compensate for the elasticdeformation of the other components of the mill, such as, roll body andneck deflection, chock deflection, screw compression, roll compression,which in the aggregate far exceeded the clastic influence of thehousings themselves, the result was that objectionable gauge variationswere experienced.

To further improve the performance of a rolling mill with respect toobtaining constant gauge, the art then developed an automatic gaugecontrol means, whereby, as the rolling load changes, the position of therolls was changed to compensate for variation in the rolling load. Anillustration of this is U.S. Patent No. 2,680,978 issued W. C. F.Hessenberg et al. on June 15, 1954. It is of interest to note that inthe Hessenberg patent reference is made to still other automatic gaugecontrol approaches which were found unsuccessful.

The most recent attempt to obtain automatic gauge control was to combinethe prestressed concept with an automatic gauge control concept whereby,as the rolling load changes, the distance between the rolls would bemaintained constant. This approach has taken two forms; one of which isillustrated in British Patent No. 955,164 for Improvements in andRelating to Rolling Mills, published on Apr. 15, 1964, and the other, asillustrated, in U.S. Patent No. 2,736,217 for Adjusting Device inRolling Mills, issued to P. Blain on Feb. 28, 1956.

In the first patent the attempt is made to maintain the distance betweenthe axes of the backup rolls or the distance between the backup chocksof a 4-high mill constant. In this construction a change in the rollingload will, if appropriate correction is not effected, change thedistance between the axes of the backup rolls. Hence, this patentteaches making an appropriate correction. The second attempt is toliterally measure the distance between the axes of the work rolls of the4-high mill and to adjust continually the rolls as the measured distanceis detected to have varied from a predetermined distance. In the firstcase, it will be noted that while the invention has eliminated not onlythe housing but the backup chocks, there still remains the elasticcharacteristics to be reckoned with, having to do with roll bending,roll compression and roll flattening. These factors are substantial and,therefore, cannot be overlooked. The second form, where the actualdistance is measured between the work rolls, has been found unacceptableas being unreliable and very cumbersome in addition to the limitationsit imposes upon the operation of the mill, say, for example, from thestandpoint of changing the rolls.

With this in mind, attention is now directed to the present inventionwhich presents a substantial improvement over the previous mills inobtaining constant gauge, several forms of which are illustrated in theaccompanying drawings of which:

FIGURE 1 is an elevational view, partly in section, of a 4-high rollingmill incorporating the features of the present invention;

FIGURE 2 is a similar view of a second embodiment of the presentinvention;

FIGURE 3 is a further embodiment of the form illustrated in FIGURE 2;

FIGURE 4 is an elevational view, partly in section, of a still furtherembodiment of the present invention;

FIGURE 5 is a further embodiment of the present in vention; and

FIGURE 6 is a typical control circuit for the mill shown in FIGURES 1-5.

With reference now to FIGURE 1, there is shown one of the housings 10 ofa 4-high mill, it being appreciated that according to normal millconstruction a similar housing will be provided for the other side ofthe mill and that it will contain all the components of the illustratedhousing. The housing 10 has a window 11 into which there is receivedbackup chocks 13 and 14 which rotatably support backup rolls 15, thebackup chocks have recesses into which there is received work rollchocks 17 and 18 that rotatably support work rolls 19 and 21. The upperbackup chock 13 is adjustable relative to the pass line of the mill by aconventional mill screw 22 received in a nut 23 secured to the housing.The motor and gear for rotating the screw are not shown since theyfollow conventional designs. Between the upper chock 13 and screw 22, asfurther noted hereinafter, there may be provided in one alternative forma load cell 24 for measuring the separating force of the mill. Accordingto usual mill designs, the backup and work roll chocks are separated bybalance cylinder assemblies 25 and 26.

Attention is now directed to the lower backup chock 14. It will be notedthat immediately below the chock there is provided a block in the formof a variable spacer and below the spacer there is provided a crosshead27. The crosshead, at its underneath surface, is engaged by the piston28 of a piston cylinder assembly 29 which is positioned betwen thebottom of the housing and the' crosshead. The cylinder is adapted to befed by a variable pressure which, at all times, either equals or exceedsthe separating force of the mill. On the two opposite sides of thecrosshead there is connected a tension rod 31 which extends downwardthrough or alongside the mill housing and at their lower ends carryspring retainer elements 32, into which there are received compressionsprings 33 The tension rods at their lower ends and beyond the retainingelements are either enlarged to form heads, or threaded to receive nuts34, and between the lower surfaces of the spring retainers and nuts areprovided load cells 35. The load cells 35 may be employed in place ofthe load cells 24, and are designed to measure the tension force imposedon the rods 31, and could take the form of conventional strain gauges,if such were desirable.

As noted above, the piston cylinder assembly 29 is adapted to apply tothe bottom roll 15 a force which may be identified as F. It will benoted that during rolling, the force F is divided into two components,one component being identified as P (the rolling force) and the othercomponent as Q (the by-pass component) which is imposed on the rods 31as a tension force, and which force eventually is transmitted to thehousing and is resisted by the reaction force of the cylinder. Thus, wefind in the illustrated mill that In the operation of the mill theinitial no-load gap condition rolls h is set by the mill screw 22, andthe force of the piston cylinder assembly 29 will act to stretch therods 31, bend the crosshead 27 and compress the springs 33, wherein theinitial hydraulic force may be identified as F and the initial force onthe rods as Q so that Q =F since P =no-load rolling force =0.

The gauge of the outgoing strip which, for purposes of description, willbe identified as t is determined by the following relationship:

P Q 114... M.

where M,,, equals the spring constant of the mill composed of rolls,backup chocks, screws, and housings, and M equals the spring constantfor the crosshead, rods, and springs. It is an object of the presentinvention, as will be later emphasized, to make the value M small byproper design of the springs with respect to M With the above remarks inmind, consideration will now be given to what takes place when a heavyor hard spot appears in the strip as it enters the roll gap. This willresult in a change in the delivery gauge of the material as representedby a change in the force P and Q,

since no change in It moving the screws takes place, such that Insubtracting Equation 2 from Equation 3 it can be seen that the change ingauge is:

M=AP (4) For Equation 4, the relationship of the change in the rollingforce P and the spring force Q to the cylinder force F in terms ofEquation 1 can be written:

which, by subtracting Equation 1 from Equation 5 the following isderived:

AF=AP+AQ Therefore, it is the prime object of the present invention toprovide a mill control wherein the variation in t=0, i.e., the roll gapof the mill is maintained constant, except for some minor factors suchas roll eccentricities. This is objective is achieved by the presentinvention by making At equal zero, in Equation 4, i.e.,

To achieve this, it follows from Equation 4 and Equation 7 that thefollowing relationship must be maintained:

s *(Mm) AP (8) Looked at another way, by defining the operatingequivalent mill stiffness as AP/ At, it follows from Equation 7 andEquation 8 that Alternatively, Equation 8 may be transformed to give sMm which, substituted in Equation 6', gives s O MJ 2) The above showsthat to make At=0, AF must be varied as AP or AQ varies to keep theratio between either AF and AP or AF and AQ constant at all times, thatis,

AF M F( Mm) A F M m A Q M t As noted above, the spring load cells 35will read AQ or the alternate load cell 24 under the screw will read AP,so that either one may be used during rolling as the actuating signaland the ratio of a change in force represented by AF/AP or AF/AQ must bemaintained, as stated in Equation 13 to obtain constant gage control.

It will be noted at this point that one of the operational advantages ofthe arrangement shown in FIGURE 1 is that the action involves no machineelements between the backup chocks since the tension rods, springs,etc., are arranged below the chocks and yield the very significantadvantage of allowing roll changing to be handled as it is presentlydone in conventional mills.

6 With reference now to the electrical-hydraulic circuit provided forsolving Equation 14 stated below, it will be noted that this formula canbe expressed in terms of a gauge error which takes the following form:

ws Q (Mm J] t where 2' equals the thickness, and e the gauge error, thatis the departure of the thickness of the rolled material from thedesired thickness, t.

It Will be appreciated that the reduction of the error in accordancewith the Equation 14 is based upon the relationship set out in Equation13, in which the relationship between the AF and AP or AQ is heldconstant when the error is made to be zero.

The control circuit illustrated in FIGURE 6 is designed to solveEquation 14, the value Q being derived from the load cells 35, the valueF from a pressure transducer 40 connected to the cylinder 29, and thevalue h from the potentiometer 41 coupled to the mill screw 22 (in FIG-URE 6 the potentiometer is shown as coupled to the motor 42 that drivesthe screw 22). The required material gauge t is set up on a manuallycontrolled potentiometer 43. Electrical signals representing h F/M 1 1 Q(MEWS) and t are summer in a summing circuit 44 to produce an errorsignal e, which is amplified in amplifier 45 and sent to adifferentiating circuit 49, the difference signal being applied to apressure control valve 51 in the supply line 52 of the cylinder toreduce the error signal to equal zero.

In referring to the other embodiments of the present invention,reference is made to FIGURE 2 where there is illustrated a housing 55having a window in which there is received backup chocks 56, the chocksadapted to rotatably support backup rolls 57, the lower chock, it beingnoted, is in engagement with a force applying piston cylinder assembly58 which exerts a force greater than the rolling load. The upper chock56 is engageable by the bottom end of a screw 59 being received in ahousing via a nut 61 in which the screw is driven in the usual Way. Thehousing is provided midway between its upper and lower portion withprojections 62 forming in a reduced window section to which there isreceived the work roll chocks 63 and, accordingly, the work rolls 64which constitute the mill.

In the usual manner, balance piston cylinder assemblies, such as 65, areprovided for the backup chocks and the work roll chocks so as to take upclearances prior to the material being introduced into the mill. In thelower portion of the projections 62 of the housing there are providedcavities 66 into which there are received readily yieldable means, suchas springs 67, the bottom surface of the springs engaging enlarged headsof plunger 68 which rest on the lower backup roll chock 56. Therelationship of the parts and the applied forces on this mill aresimilar to the mill of FIGURE 1 and may be represented as F =P+Q Where Fis the cylinder force, P, the rolling force, and Q, the compressionforce on the spring. A AP signal will be developed as in the alternateform illustarted in FIGURE 1 from a load cell 69 arranged between thescrew 59 and the upper chock 56.

Aside from these distinctions the embodiments in FIG- URE 2 will besimilar to the arrangement in FIGURE 1.

With reference to FIGURE 3, which illustrates a further embodiment and asecond embodiment of the principle illustrated in FIGURE 2, and in whichonly the lower half of the mill in FIGURE 2 is illustrated, wherein itwill be noted that the projections 71 of the housing are located at thebottom of the housing. In these projections there are provided cavities72 for receiving springs 73 as in the case of FIGURE 2. The lower end ofthe springs engage enlarged heads of plunger 74 which are carried by acrosshead 75 forming the cylinder of a piston cylinder assembly 76, thepiston being in engagement with the bottom of the housing. Between thecrosshead and the bottom chock there are provided variable spacers 77 totake care of a change in the diameter of the roll. The mill arrangementin FIGURE 3, aside from the structural dilterences, is similar inoperation as that disclosed with respect to the FIGURE 2 embodiment.

The embodiment of the present invention illustrated in FIGURE 4 will nowbe described. It will be appreciated that while the equipment to bediscussed is arranged at the bottom of the mill, it can be just as wellarranged at the top. With reference to this figure there is provided ahousing 81 which has a window 82 into which there is received backupchocks 83 of a 4-high mill, backup chocks rotatably supporting backuprolls 84. The backup chocks, as in the case of FIGURE 1, are providedwith cavities 85 into which there are received work roll chocks 86 whichrotatably support work rolls 87. The backup and work roll chocks areprovided with the usual balance cylinder assemblies 88 and 89. The upperbackup chock is adapted to be adjusted by a mill screw, not shown, whichis driven in the usual way. With respect to the lower backup chock 83,it will be noted that it is provided with projections 91 that provide anopening for receiving the ends of the tension bars 92, the tension barsextending downward through or alongside the mill and are connected to acommon crosspiece 93. The crosspiece itself is movable towards and awayfrom the rolls by a power-driven screw '94 which is connected to a wormwheel 95 driven by a worm 96, the drive for the worm not being shown.The screw 94, it will be noted, engages the bottom of the housing 81.The screw can be operated to maintain the pass line, set the initialroll gap, or change the gap during rolling. Between the lower backupchock and the housing is provided a piston cylinder assembly 97 adaptedas in the other embodiments to deliver a force greater than the rollingload and which pressure is changed pursuant to the formula F =P+Q.

As pointed out above, while the present invention and the novelmechanism illustrated and described have been set forth as a procedurefor obtaining constant roll gap, should for any reason the rolling millillustrated be desired to be operated with a constant cylinder pressure,this can be performed. Also, should it be desired, in accordance withpresent practice, to operate the mill whereby the Q force in the formulaF=P+Q (Equation 1) is maintained constant, thereby, as for example inFIGURE 1, maintain the distance between the backup rolls constant, thismethod can also be carried out in the present invention withoutnecessitating any change aside from what is required to control thecylinder in FIGURE 6 to maintain the cell reading constant. It will alsobe noted, as illustrated in FIGURES 1 and that while in a givenconstruction it may be desirable to provide readily yieldable means,such as springs, for maintaining a desired relationship between themoduli of the rolling mill parts subject to the rolling pressure, andthe rolling mill parts subject to the Q force, this is not necessary incertain applications as illustrated in FIGURE 4.

It will be appreciated that the relationship of the spring or otheryieldable means, such as tension rods, with reference to the cylindercan be changed from what is shown in FIGURES 1 and 4, so that the springforce acts in the same direction as the force of the cylinder. In thisconstruction the cylinder force will be less than the rolling force byan amount equal to the spring force. In FIG- URE 5 there is illustratedsuch an arrangement, wherein there is shown a housing 101 having awindow 102 that receives the rolls shocks of a 4-high mill. The upperchock is engaged by a cross member which is urged downward by a pair offorce applying cylinders 104. At the center of the cross member a spring105 is rotated between the cross member and a screw 106, which is drivenby a motor wheel set 107. In this arrangement the spring and cylinderact in concert, the force of the cylinder being controlled by the signalof a load cell 108 as in the other embodiments.

In accordance with the provisions of the patent statutes, I haveexplained the principle and operation of my invention and haveillustrated and described what I consider to represent the bestembodiment thereof. However, I desire to have it understood that withinthe scope of the appended claims, the invention may be practicedotherwise than as specifically illustrated and described.

I claim: 1. In a rolling mill, or like apparatus having a housing, anelongated window in said housing, and

a pair of rolls between which a rolling force is developed, includingmounting means for each roll received in said window of said housing,wherein a portion of the housing receiving the mounting means and atleast one of said mounting means is subject only to the rolling force ofthe mill,

means arranged at one end of said window of said housing and between oneof the mounting means and housing for applying to a first group of millparts, including one of said mounting means, a substantial part of aroll gap controlling force, said force being applied in a direction toresist the rolling force of the mill,

the force applying means being constructed and arranged so that theforce differential between its total force and the rolling force isapplied to a second group of mill parts, which excludes at least saidother mounting means, and wherein the elastic characteristics of saidtwo groups of mill parts have a predetermined relationship.

2. In a rolling mill according to claim 1, wherein said second group islocated in the one extreme of said window and outside the area definedby said mounting means and having a tension member for transmitting saiddifferential force between said force applying means and said housing.

3. In a rolling mill according to claim 1, including a control means forcontinually measuring the force imposed on either said first or secondgroup of parts and varying the applying force proportional to a changein the force being imposed on said first or second group of mill partsto maintain a predetermined relationship be tween either of these forcesand the applied force.

4. In a rolling mill, or like apparatus, having housings, and

a pair of rolls between which a rolling force is developed includingmounting means for each roll,

means arranged in said housings at one side thereof for applying to afirst group of mill parts, including said mounting means, a substantialpart of a roll gap controlling force, said force being applied in adirection to resist the rolling force of the mill,

the force applying means being constructed and arranged so that theforce difierential between its total force and the rolling force isapplied to a second group of mill parts, which excludes at least one ofsaid mounting means, and wherein the elastic characteristics of said twogroups of mill parts have a predetermined relationship,

means separate from said force applying means and associated with themounting means arranged on the sides of the housings opposite said forceapplying means for adjusting the associated mounting means and its rollto adjust the position of the roll independent of said force applyingmeans.

5. In a rolling mill according to claim 4, including a control means forcontinually measuring the force imposed on either said first or secondgroup of parts and varying the applying force proportional to a changein the force being imposed on said first or second group of mill partsto maintain a predetermined relationship between either of these forcesand the applied force.

6. In a rolling mill according to claim 1, said second group of millparts comprises one or more tension rods associated with the lowest rollassembly of the mill, said tension rod subject to a tension force bysaid force applying means, and wherein the tension imposed on saidtension rods is measured by a force measuring means.

7. In a rolling mill according to claim 6, wherein a readily yieldablemeans is associated with said tension rods and arranged to be compressedthereby to give added flexibility to said second group of mill parts.

8. In a rolling mill according to claim 6, including a force measuringdevice associated with said housing arranged to receive and measure theseparating force of said roll assemblies.

9. In a rolling mill according to claim 1, including readily yieldablemeans received in the housing of said mill and so associated with theforce applying means to be subject to a compression force.

10. In a rolling mill according to claim 9, wherein said housing isprovided with projections, openings in said projections for receiving aplurality of springs, one end of said springs engaging one of said rollchocks of the roll assembly, said springs being compressed by theapplication of said force applying means and wherein said housingprojections are in the vicinity of the work rolls of the mill.

11. In a rolling mill according to claim 1, including a rotatable screwassociated with one of said rolls for adjusting the initial gap of saidroll assemblies.

12. In a rolling mill according to claim 9, in which said housing isprovided with projections located at the base of the mill, theprojections including openings for receiving springs and wherein saidsprings engage a member associated with said force applying means andare compressed upon movement thereof.

13. In a rolling mill according to claim 1, comprising a pair ofsubstantially parallel arms connectable at one of their ends to one ofthe roll chocks of the mill and at the other of their ends to a crossmember, means for adjusting the cross member relative to the pass lineof the mill in which construction the force applying means in applying aforce on the roll chock to which the arms are associated imposes atension force on said arms, a'portion of which is taken into the crossmember and into the housing.

14. In a rolling mill according to claim 1, including a cross memberarranged in said window and between a mounting means of one of saidrolls and said housing,

said force applying means arranged between said cross member and saidhousing,

a rotable screw mounted in said housing on the same said thereof thatsaid force applying means is located, and

a yieldable means arranged between the screw and said cross member.

References Cited UNITED STATES PATENTS 3,327,508 6/1967 Brown 72-243CHARLES W. LANHAM, Primary Examiner L. A. LARSON, Assistant Examiner US.Cl. X.R. 712 1, 245

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,496,743 February 24, 1970 Morris Denor Stone It is certified thaterror appears in the above identified patent and that said LettersPatent are hereby corrected as shown below:

Column 4, line 45,"(the bypass component)" should read (the by-passforce component) Column 5, equation 11, should appear as shown below:

AP vAQ equation 12, should appear as shown below:

M AP 6 AQ Column 6, line 34, "summer" should read summed Column 10, line22, "said" should read side Signed and sealed this 16th day of February1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

